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Water level response in wells to dynamic shaking in confining unconsolidated sediments: a laboratory study

Citation

Gu, Hongbiao et al. (2020), Water level response in wells to dynamic shaking in confining unconsolidated sediments: a laboratory study, Dryad, Dataset, https://doi.org/10.5061/dryad.c59zw3r51

Abstract

This article focuses on laboratory experiments designed to investigate the influence of dynamic shaking on water level fluctuation in wells of unconsolidated sediments. A large flume filled with natural sandy sediments was subjected to horizontal dynamic loading at different frequencies (0.5-15Hz) and accelerations (0.1g, 0.15g, 0.25g and 0.5g), generated by a shaking table. Thus, the change in characteristics of the water and saturated sediments were investigated, including how water level and hydraulic properties changed over time, are of significant interest. A range of water level changes following the oscillating pore pressure for hydrostatic and hydrodynamic (flowing) conditions were observed: oscillation, step-rise, step-rise with oscillation, and step-drop with oscillation, similar to those observed in nature after earthquakes. We find that water level declines occur when the imposed frequency is less than 2Hz, while the acceleration has weak correlation on the water level change when it is less than 0.5g. Sinusoidal wave propagation reduces hydraulic conductivity first sharply which then stabilizes at a constant value with a slight increase.  Heterogeneous consolidation, mechanical resonance, compaction, dilation, and re-packing of the grain structure may constitute a physically plausible mechanism for water level fluctuations and hydraulic parameters adjustment. Laboratory experiments can therefore provide quantitative and process-oriented approach to better understand water level response to seismic waves.This article focuses on laboratory experiments designed to investigate the influence of dynamic shaking on water level fluctuation in wells of unconsolidated sediments. A large flume filled with natural sandy sediments was subjected to horizontal dynamic loading at different frequencies (0.5-15Hz) and accelerations (0.1g, 0.15g, 0.25g and 0.5g), generated by a shaking table. Thus, the change in characteristics of the water and saturated sediments were investigated, including how water level and hydraulic properties changed over time, are of significant interest. A range of water level changes following the oscillating pore pressure for hydrostatic and hydrodynamic (flowing) conditions were observed: oscillation, step-rise, step-rise with oscillation, and step-drop with oscillation, similar to those observed in nature after earthquakes. We find that water level declines occur when the imposed frequency is less than 2Hz, while the acceleration has weak correlation on the water level change when it is less than 0.5g. Sinusoidal wave propagation reduces hydraulic conductivity first sharply which then stabilizes at a constant value with a slight increase.  Heterogeneous consolidation, mechanical resonance, compaction, dilation, and re-packing of the grain structure may constitute a physically plausible mechanism for water level fluctuations and hydraulic parameters adjustment. Laboratory experiments can therefore provide quantitative and process-oriented approach to better understand water level response to seismic waves.

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